1. Field of the Invention
The present invention generally relates to a printing apparatus and, more specifically, to a printing apparatus having a thermal head, a platen roller pressing a sheet against the thermal head, and a printing apparatus having the thermal head, the platen roller, and a cutting device for cutting a printed sheet.
2. Description of the Related Art
FIG. 1 shows a typical conventional thermal printing apparatus 1. The thermal printing apparatus 1 includes a printer main body 2 and a module 20 mounted on the printer main body 2. It should be noted that, in the accompanying figures, the arrows, X1-X2, Y1-Y2, and Z1-Z2 indicate the longitudinal, the depth, and the height directions, respectively, of the thermal printing apparatus 1.
As shown in FIGS. 1 through 3, the printer main body 2 includes a frame 3 having its side plates 3X1 and 3X2, a first pulse motor 4 for driving a platen roller and a second pulse motor 5 for driving a cutting device, a thermal head 6 and a stationary blade 7 each provided in the middle of the frame 3, first and second reduction gear drive mechanisms 8 and 9, and covers 10 and 11. The first and the second reduction gear drive mechanisms 8 and 9 reduce the rotational speed of the first and the second pulse motors 4 and 5 and transmit the rotational motion to the outside of the side plates 3X1 and 3X2 of the frame 3, and are covered by the covers 10 and 11, respectively.
Grease is applied to the reduction gear drive mechanisms 8 and 9. As shown in FIG. 2, the gears 12 and 13 of the first and the second reduction gear drive mechanisms 8 and 9 are the final gears of the first and the second reduction gear drive mechanisms 8 and 9, respectively. The covers 10 and 11 have openings 10a and 11a in the vicinity of the gears 12 and 13, respectively.
As shown in FIG. 1, the module 20 includes a frame 21, a platen roller 22 rotatably mounted on the frame 21 and having a gear 24 on one end, a movable blade 23 slidably mounted on the frame 21, and a reduction gear drive mechanism 25 mounted on the flange of the platen roller 22. The reduction gear drive mechanism 25 includes gears 26, 27, and 28. The gear 28 is the final gear meshed with a rack 29 integrally formed with the movable blade 23.
The printing apparatus 1 is configured by mounting the module 20 on the printer main body 2. When the module 20 is mounted on the printer main body 2, the platen roller 22 is pressed against the thermal head 6 with a sheet interposed in between, the movable blade 23 faces the stationary blade 7, and the gears 24 and 25 are meshed with the gears 12 and 13, respectively.
When a printing instruction is issued, the thermal head 6 and the first pulse motor 4 are driven so as to rotate the platen roller 22 through the reduction gear drive mechanism 8 and the gear 24, print a sheet by the thermal head 6, and feed the sheet by the platen roller 22. When a cutting instruction is issued, the second pulse motor 5 is driven so as to move the movable blade 23 through the reduction gear drive mechanisms 8 and 25 and the rack 29, and cut the fed sheet from the printer apparatus 1.    Patent Document 1: Japanese Patent Application Publication No.: 2005-081774
However, there is a problem that since there are the openings 10a and 11a formed on the covers 10 and 11 covering the reduction gear drive mechanisms 8 and 9, respectively, when the printing apparatus 1 is used in a dusty working environment, the reduction gear drive mechanisms 8 and 9 are susceptible to dust contamination, thereby easily wearing the gears to shorten the service life. Also, disadvantageously, the grease applied to the reduction gear drive mechanisms 8 and 9 attracts and contains the dust entering inside the covers 10 and 11, thereby accelerating the wearing of the gears. When the wearing of the gears proceeds, the service life of the printing apparatus 1 becomes shorter accordingly.
Further, as shown in FIG. 2, there is another problem that since the reduction gear drive mechanisms 8 and 9 are disposed outside the side plates 3X1 and 3X2, respectively, the length L2 extended outward from the flanges 2a and 2b reaches about 20 mm. As a result, the length L1 in the longitudinal direction disadvantageously reaches about 130 mm.
On the other hand, this type of thermal printing apparatus 1 is often embedded in a portable ticketing system and the length L1 in the longitudinal direction of the printing apparatus 1 substantially defines the width of the portable ticketing system. However, there is a demand for reducing the size of portable ticketing systems to make them more portable. Therefore, the length L1 in the longitudinal direction of the printing apparatus 1 is required to be reduced as much as possible.